Mandrels and methods for abrasive flow machining

ABSTRACT

A method for smoothing surface roughness within a passageway is disclosed. In various embodiments, the method comprises flowing an abrasive media through the passageway and positioning a mandrel within the passageway, the mandrel being sized to create a gap between an outer surface of the mandrel and an inner surface of the passageway, wherein the abrasive media is caused to flow through the gap, abrading the inner surface of the passageway.

FIELD

The present disclosure relates generally to methods of finishing internal portions of additively manufactured components and, more particularly, to methods and apparatus in which a mandrel is used to smooth walls of passageways extending within additively manufactured components.

BACKGROUND

Fabrication processes such as additive manufacturing enable fabrication of article geometries that are difficult or otherwise impossible to make by other fabrication techniques. For example, components in gas turbine engines may include internal passages for conveying coolants or lubricants. Additive manufacturing and other advances permit such passages to be formed having complex geometries within thin wall structures and having high-aspect ratios. However, due to the additive manufacturing process, and even with other fabrication processes, the surfaces of these passages can be rough following the fabrication process. If left in the final component, this surface roughness has the potential to interfere with fluid flow through the passageways.

Abrasive machining is a technique used to smooth surface roughness on the inner surfaces of conduits or passageways in additively manufactured components. The technique involves forcing an abrasive media through the conduits or passageways to abrade or wear away the surface roughness on the inner surfaces. In certain instances, however, a steep velocity gradient can develop within the conduit or passageway, resulting in the abrasive material flowing freely within a center region of the conduit or passageway and flowing very slowly or not at all near the surfaces requiring smoothing. The phenomena may be characterized, in various situations, as a Poiseuille-type flow through a pipe, where the velocity of the fluid is greatest near the center of the pipe and approaches zero near the boundary of the pipe.

SUMMARY

A method for smoothing surface roughness within a passageway is disclosed. In various embodiments, the method comprises flowing an abrasive media through the passageway and positioning a first mandrel within the passageway, the first mandrel being sized to create a gap between an outer surface of the first mandrel and an inner surface of the passageway, the abrasive media being caused to flow through the gap, abrading the inner surface of the passageway.

In various embodiments, the first mandrel is positioned at different locations within the passageway during a first smoothing operation. In various embodiments, positioning the first mandrel at different locations occurs through a passive process by action of friction between the outer surface of the first mandrel and the inner surface of the passageway. In various embodiments, the abrasive media is caused to flow in a forward direction followed by a reverse direction. In various embodiments, the first smoothing operation if followed by a second smoothing operation using a second mandrel, the second mandrel being sized larger than the first mandrel.

In various embodiments, the first mandrel is connected to a cable configured to position the first mandrel at different locations. In various embodiments, the cable is connected to a cable reel configured to pay out the cable in a downstream direction. In various embodiments, the cable reel is configured to withdraw the cable in an upstream direction. In various embodiments, the passageway includes a circular cross section and the first mandrel is a first sphere. In various embodiments, a second sphere is connected to the cable adjacent the first sphere.

In various embodiments, a first smoothing operation comprises traversing the first mandrel from an inlet of the passageway to an exit of the passageway followed by traversing the first mandrel from the exit of the passageway to the inlet of the passageway. In various embodiments, traversing the first mandrel from the exit of the passageway to the inlet of the passageway is caused to occur by withdrawing a cable connected to the first mandrel. In various embodiments, traversing the first mandrel from the exit of the passageway to the inlet of the passageway is caused to occur by reversing a flow direction of the abrasive media. In various embodiments, the first mandrel includes a non-spherical shape.

An apparatus for smoothing surface roughness within a passageway is disclosed. In various embodiments, the apparatus includes an abrasive flow machine configured to pump abrasive media through a component having the passageway and a mandrel configured for variable positioning along a length within the passageway, the mandrel being sized to create a gap between an outer surface of the mandrel and an inner surface of the passageway.

In various embodiments, the mandrel is sized to enable friction between the outer surface of the mandrel and the inner surface of the passageway to control the variable positioning. In various embodiments, that apparatus further includes a cable reel and a cable connected to the mandrel, the cable reel being configured to control the variable positioning. In various embodiments, the passageway includes a circular cross section and the mandrel is a sphere.

A method for smoothing surface roughness within a passageway is disclosed. In various embodiments, the method comprises the steps of, positioning a mandrel within the passageway, the mandrel being sized to create a gap between an outer surface of the mandrel and an inner surface of the passageway; flowing an abrasive media through the passageway in a first direction; and moving the mandrel in the first direction, the abrasive media being caused to flow through the gap, abrading the inner surface of the passageway upstream of the mandrel. In various embodiments, the passageway and the mandrel have a non-circular cross section and the positioning of the mandrel is controlled by a rod connected to a downstream portion of the mandrel.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the following detailed description and claims in connection with the following drawings. While the drawings illustrate various embodiments employing the principles described herein, the drawings do not limit the scope of the claims.

FIG. 1 is a cross sectional schematic view of a gas turbine engine, in accordance with various embodiments;

FIG. 2 is a cross sectional schematic view of a passageway extending through the interior of an additively manufactured part, in accordance with various embodiments;

FIG. 3A is a schematic representation of an abrasive flow machining system configured to smooth a passageway extending through the interior of an additively manufactured part, in accordance with various embodiments;

FIGS. 3B, 3C and 3D are cross sectional schematic views of the internal passageway illustrated in FIG. 3A undergoing abrasive flow machining, in accordance with various embodiments;

FIG. 4A is a schematic representation of an abrasive flow machining system configured to smooth a passageway extending through the interior of an additively manufactured part, in accordance with various embodiments;

FIGS. 4B, 4C, 4D and 4E are cross sectional schematic views of the internal passageway illustrated in FIG. 4A undergoing abrasive flow machining, in accordance with various embodiments;

FIGS. 5A, 5B and 5C are axial, side and top schematic views, respectively, of a mandrel configured to smooth a passageway having a non-circular cross sectional geometry, in accordance with various embodiments; and

FIGS. 5D and 5E are schematic cross sectional views of the mandrel illustrated in FIGS. 5A, 5B and 5C being used to smooth a passageway having a non-circular cross sectional geometry, in accordance with various embodiments.

DETAILED DESCRIPTION

The following detailed description of various embodiments herein makes reference to the accompanying drawings, which show various embodiments by way of illustration. While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that changes may be made without departing from the scope of the disclosure. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected, or the like may include permanent, removable, temporary, partial, full or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. It should also be understood that unless specifically stated otherwise, references to “a,” “an” or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural. Further, all ranges may include upper and lower values and all ranges and ratio limits disclosed herein may be combined.

Referring now to the drawings, FIG. 1 schematically illustrates a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section 22 drives air along a bypass flow path B in a bypass duct defined within a nacelle 15, while the compressor section 24 drives air along a primary or core flow path C for compression and communication into the combustor section 26 and then expansion through the turbine section 28. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it will be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines, including three-spool architectures.

The gas turbine engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems at various locations may alternatively or additionally be provided and the location of the several bearing systems 38 may be varied as appropriate to the application. The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a low pressure compressor 44 and a low pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in this gas turbine engine 20 is illustrated as a fan drive gear system 48 configured to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a high pressure compressor 52 and a high pressure turbine 54. A combustor 56 is arranged in the gas turbine engine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46 and may include airfoils 59 in the core flow path C for guiding the flow into the low pressure turbine 46. The mid-turbine frame 57 further supports the several bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via the several bearing systems 38 about the engine central longitudinal axis A, which is collinear with their longitudinal axes.

The air in the core flow path is compressed by the low pressure compressor 44 and then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, and then expanded over the high pressure turbine 54 and low pressure turbine 46. The low pressure turbine 46 and the high pressure turbine 54 rotationally drive the respective low speed spool 30 and the high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, the compressor section 24, the combustor section 26, the turbine section 28, and the fan drive gear system 48 may be varied. For example, the fan drive gear system 48 may be located aft of the combustor section 26 or even aft of the turbine section 28, and the fan section 22 may be positioned forward or aft of the location of the fan drive gear system 48.

Various components of the gas turbine engine 20 include conduits or passageways extending through the component or a portion thereof. For example, components in the gas turbine engine 20 may include internal passages for conveying a coolant. Such components include, for example, the blades and the stators that comprise the compressor and turbine sections described above. Such components may also comprise passageways for conveying bleed air from the compressor to other areas of the gas turbine engine 20 benefitting from a source of high-pressure cooling fluid. Other components comprising conduits or passageways include the lubrication system, where lubricants are delivered from a pump to bearings and the like. Many of these various components are constructed using additive manufacturing techniques and include conduits or passageways having curved portions with rough internal surfaces following their manufacture.

Referring now to FIG. 2, a component 200, fabricated through additive manufacture, is illustrated. The component 200 includes a passageway 202 extending from a first end 204 to a second end 206. The passageway 202 is defined by an inner surface 208 that, in various embodiments, is generally circular in cross section from the first end 204 to the second end 206. As illustrated, the inner surface 208 of the passageway 202 may be characterized by an undesirable degree of surface roughness following initial fabrication through additive manufacture. In various embodiments, the passageway 202 is curved at one or more portions along a length defined by an arc-length distance from the first end 204 to the second end 206. As illustrated, for example, the passageway 202, in various embodiments, includes a first substantially straight portion 210 downstream of the first end 204, followed by a curved U-shaped portion 212 downstream of the first substantially straight portion 210, which is followed by a second substantially straight portion 214 upstream of the second end 206. In various embodiments, the passageway 202 is characterized by an aspect ratio (e.g., a characteristic length 216 of the passageway divided by a characteristic lateral dimension, such as, for example, a diameter 218 of the passageway). In various embodiments, the aspect-ratio may have a value greater than four (4); in various embodiments, the aspect-ratio may have a value greater than ten (10); and in various embodiments, the aspect-ratio may have a value greater than twenty-five (25). While various embodiments of the disclosure are described using a simplified component and passageway, such as the component 200 and passageway 202 just described, the disclosure contemplates embodiments with passageways having any number of curved or straight portions within a component. The disclosure that follows provides a method to reduce the surface roughness of the passageway 202 within the component 200, or other components having various numbers of curved or straight passageways therein.

Referring now to FIG. 3A, an abrasive flow machine 350 is illustrated and used to describe an apparatus and method for abrasive flow machining, according to various embodiments. As illustrated, the abrasive flow machine 350 includes a pump 352 that is fluidly connected to a tube network 354. The tube network 354 includes one or more tubes 356 for conveying an abrasive media, represented by flow F. The tube network 354 may include one or more valves 358 to control the direction of the flow F in the tube network 354, as well as one or more receptacles 360 for collecting used abrasive media.

A component 300, such as the component 200 with the passageway 202 described above with reference to FIG. 2, is operably configured within a flow circuit comprising the tube network 354 and a passageway 302 of the component 300. The passageway 302 includes a first end 304 or entrance and a second end 306 or exit that may be connected to the tube network 354 using suitable fluid connectors. As will be appreciated, the entrance and exit of the passageway 302 may change, depending upon the direction of flow F of the abrasive media. In various embodiments, the passageway 302 is characterized by an aspect ratio having a value greater than four (4) which, in various embodiments, may be considered a high aspect ratio. Generally, increasingly higher aspect ratios cause increasingly higher pressure drop of the flow of abrasive media from entrance to exit. The pump 352 is operable in the method to move the abrasive media, as flow F, through a portion of the tube network 354, into the passageway 302, and then back into another portion of the tube network 354. The direction of flow F through the passageway 302 may be reversed by changing the position of the one or more valves 358. The method may therefore include multiple bidirectional flow cycles through the passageway 302 to polish the passage surfaces.

As mentioned above, increasingly higher aspect ratios of the passageway 302 may cause increasingly higher pressure drop of the flow F of abrasive media across the length of the passageway 302. In this regard, the abrasive media of the method may have a low-viscosity formulation that enables the pump 352 to move the abrasive media through the passageway 302. For example, the abrasive media may include a carrier liquid material and solid particulate (abrasive material). In various embodiments, the carrier liquid is, without limitation, one or more of water, a solvent and a liquid hydrocarbon, or mixtures thereof. In various embodiments, the solid particulate may be, but is not limited to, one or more of silicon carbide and aluminum oxide, or mixtures thereof.

As also described above, in various embodiments, a steep velocity gradient can develop within the passageway 302, resulting in the abrasive material flowing freely within the interior or center of the passageway 302 and flowing very slowly or not at all near the inner surfaces requiring smoothing—e.g., near an inner surface 308 of the passageway 302. Accordingly, in various embodiments, a mandrel—e.g., a sphere 370—is placed within the fluid circuit, comprising the tube network 354 and the passageway 302 of the component 300, to tailor the flow characteristics of the abrasive media to more effectively abrade the inner surface 308. As described further below, as the sphere 370 is forced through the passageway 302 by the abrasive media, a leakage flow of abrasive media between an outer surface 372 of the sphere 370 and the inner surface 308 of the passageway 302 is established, which focuses the abrading effect of the abrasive media away from the interior or center of the passageway 302 and toward the inner surface 308 of the passageway 302.

Referring to FIGS. 3B, 3C and 3D a series of drawings illustrates a progression of the smoothing of the passageway 302 as the sphere 370 traverses the passageway 302 from the first end 304 to the second end 306. Starting with FIG. 3B, the sphere 370 is illustrated entering the passageway 302 at the first end 304. The diameter of the sphere 370 is sized with respect to the diameter of the passageway 302 to establish a gap 374 between the outer surface 372 of the sphere 370 and the inner surface 308 of the passageway 302. In various embodiments, the gap 374 extends about the sphere 370 and provides a narrow passage for the flow of abrasive media 376 to be forced along the inner surface 308 of the passageway 302. Forcing the abrasive media 376 through the gap 374 results in the abrading effect of the abrasive media 376 to focus on the inner surface of the passageway 302 rather than merely flowing through the interior or center of the passageway 302 where little to no abrasion occurs. In various embodiments, the gap 374 is sized such that friction between the outer surface 372 of the sphere 370 and the inner surface 308 of the passageway 302 passively controls the position of the sphere 370 within the passageway 302. More specifically, as the inner surface 308 of the passageway 302 is abraded, the size of the passageway 302—e.g., the diameter of the passageway 302—adjacent the sphere 370 increases, thereby reducing friction between the respective surfaces of the sphere 370 and the passageway 302 and enabling the sphere 370 to travel progressively along the length of the passageway 302 as the smoothing operation continues. In various embodiments, the gap 374 may have a non-dimensional radial dimension of one (1) to five (5) one-hundredths the diameter of the sphere 370. In various embodiments, the gap 374 may have a size equal from about one-hundred (100) microns (≈3.93 E-03 inches) to about two-thousand (2000) microns (≈7.87 E-02 inches).

Referring to FIG. 3C, the sphere 370 is illustrated having traversed a first substantially straight portion 310 of the passageway 302, downstream of the first end 304. A smoothed region 378 of the inner surface 308 of the passageway 302 is present upstream of the sphere 370 by action of the abrasive media 376 flowing through the gap 374 as the sphere 370 traverses along the passageway 302, while a non-smoothed region 380 remains downstream of the sphere 370. Referring to FIG. 3D, the sphere 370 is illustrated as having traversed a curved U-shaped portion 312 of the passageway 302, downstream of the first substantially straight portion 310, and nearly the length of a second substantially straight portion 314 upstream of the second end 306. As illustrated, as the sphere 370 progresses the passageway, the smoothed region 378 increases in length along the length of the passageway 302 while the non-smoothed region 380 decreases in length.

Once the sphere 370 approaches or exits the second end, the abrasive flow machine 350 may be turned off and the component 300 removed from the machine. Alternatively, in various embodiments, the pump 352 may be reversed, forcing the sphere 370 back to the first end 304 for additional smoothing in the opposite direction as that just described. In various embodiments, the process may be repeated using progressively larger spheres until a desired smoothing is obtained. In various embodiments, multiple spheres, having the same dimensions as the sphere 370 above described, or even dissimilar dimensions among the multiple spheres, may be forced through the passageway 302 simultaneously, as a progression of spheres, providing a further enhancement of the smoothing effect of the abrasive media as it and the spheres are forced through the passageway 302 by action of the abrasive flow machine 350.

Referring now to FIG. 4A, an abrasive flow machine 450 is illustrated and used to describe an apparatus and method for abrasive flow machining, according to various embodiments. The abrasive flow machine 450 includes similar components described above in regard to the abrasive flow machine 350 referenced in FIG. 3A, including a pump 452 fluidly connected to a tube network 454, one or more tubes 356 for conveying an abrasive media, represented by flow F, one or more valves 458 to control the direction of the flow F in the tube network 454, and one or more receptacles 460 for collecting used abrasive media. The abrasive flow machine 450 further includes a cable mechanism 462. In various embodiments, the cable mechanism 462 includes a cable 464 having a first end 466 connected to a sphere 470, similar to the sphere 370 above described with reference to FIGS. 3A-3D, and a second end 468 connected to a cable reel 469. In various embodiments, a sheave 465 or similar device may be used to guide the cable 464 from the cable reel 469 to the sphere 470.

A component 400, such as the component 200 with the passageway 202 described above with reference to FIG. 2, is operably configured within a flow circuit comprising the tube network 454 and a passageway 402 of the component 400. The component 400 and the passageway 402 include various of the features above described with reference to the component 300 and the passageway 302 illustrated in FIGS. 3A-3D, which are not repeated here. Referring, thus, to FIGS. 4B, 4C and 4D a series of drawings illustrates a progression of the smoothing of the passageway 402 as the sphere 470 traverses from a first end 404 to a second end 406 of the passageway 402.

Starting with FIG. 4B, the sphere 470 is illustrated entering the passageway 402 at the first end 404. Unlike the embodiment above described, the cable 464 is used to maintain the sphere 470 at a desired position in the passageway against the force of the flow F of the abrasive media 476. The cable 464 provides more flexibility in selecting the size of a gap 474 that extends about the sphere 470 and provides a narrow passage for the flow of abrasive media 476 to be forced between an outer surface 472 of the sphere 470 and an inner surface 408 of the passageway 402. A close-up view of the gap 474, the sphere 470 and the various surfaces just described (in addition to those described above with reference to FIGS. 3B-3D) is provided in FIG. 4E. Because the cable 464 maintains the sphere 470 in position within the passageway 402, in contrast to friction maintaining the sphere 370 above described in position within the passageway 302, a gap 474 larger is size may be maintained than the gap 374 above described with reference to FIGS. 3B-3D. In various embodiments, for example, the gap 474 may have a non-dimensional radial dimension of one (1) to ten (10) one-hundredths the diameter of the sphere 470. In various embodiments, the gap 474 may have a size equal from about five-hundred (500) microns (≈1.96 E-02 inches) to about five-thousand (5000) microns (≈1.96 E-01 inches).

Referring to FIG. 4C, the sphere 470 is illustrated having traversed a first substantially straight portion 410 of the passageway 402, downstream of the first end 404. A smoothed region 478 of the inner surface 408 of the passageway 402 is present upstream of the sphere 470 by action of the abrasive media 476 flowing through the gap 474 as the sphere 470 traverses along the passageway 402, while a non-smoothed region 480 remains downstream of the sphere 470. Referring to FIG. 4D, the sphere 470 is illustrated as having traversed a curved U-shaped portion 412 of the passageway 402, downstream of the first substantially straight portion 410, and nearly the length of a second substantially straight portion 414 upstream of the second end 406. As illustrated, as the sphere 470 progresses the passageway, the smoothed region 478 increases in length along the length of the passageway 402 while the non-smoothed region 480 decreases in length.

Once the sphere 470 approaches or exits the second end, the abrasive flow machine 450 may be turned off and the component 400 removed from the machine. Alternatively, in various embodiments, the cable reel 469 reverses direction and, rather than paying out the cable 464 to allow the sphere 470 to flow downstream against the flow F of abrasive media 476, the cable 464 is used to pull the sphere upstream against the flow F of the abrasive media 476. The process may be repeated as required until a desired smoothness is achieved. In various embodiments, the process may be repeated using progressively larger spheres until a desired smoothing is obtained. In various embodiments, multiple spheres, having the same dimensions as the sphere 470 above described, or even dissimilar dimensions among the multiple spheres, may be forced through the passageway 402 simultaneously, as a progression of spheres, providing a further enhancement of the smoothing effect of the abrasive media as it and the spheres are forced through the passageway 402 by action of the abrasive flow machine 450. In various embodiments, the multiple spheres may be arranged similar to pearls on a neckless, with a first sphere secured to the cable 464 and the remaining spheres threaded on to the cable, with the cable running through holes drilled through the spheres.

Referring now to FIGS. 5A-5E, a mandrel configured to smooth a non-circular passageway is illustrated and described, according to various embodiments. By non-circular, the disclosure contemplates passageways and corresponding mandrels having, for example, square, rectangular, polygonal, oval and other non-circular shaped cross sectional geometries. Specifically, and without loss of generality, FIGS. 5A, 5B and 5C provide axial, side and top schematic views, respectively, of a mandrel 500 configured to smooth a passageway having a non-circular cross sectional geometry, in accordance with various embodiments. As illustrated in the axial view of FIG. 5A, for example, and without loss of generality, the mandrel 500 includes a bottom portion 502, a top portion 504 a first side portion 506 and a second side portion 508. The bottom portion 502 is generally flat, while the top portion 504 has a generally flat portion 510 and a protruding portion 512. The first side portion 506 has a semi-circular shape, while the second side portion 508 includes a generally flat shape that smoothly merges into the bottom portion 502 and the protruding portion 512. Referring to FIGS. 5B and 5C, the mandrel 500 also includes a front portion 514 and a rear portion 516. In various embodiments, a rod 518 is connected to the rear portion 516.

Referring now to FIGS. 5D and 5E, the mandrel 500 is illustrated traversing a passageway 520 having a non-circular shape. Similar to the mandrel 500, the passageway 520 includes respective bottom 522, top 524 and protrusion 526 portions. Referring to FIG. 5D, the mandrel 500 is positioned at an upstream position with respect to an abrasive medial 530 flowing from left to right; referring to FIG. 5E, the mandrel is shown positioned slightly farther downstream than the position shown in FIG. 5D. In various embodiments, the rod 518 is connected to a positioning device that controls the position of the mandrel 500 within the passageway 520. In various embodiments, the rod 518 is positioned downstream of the mandrel 500 with respect to the direction of flow of the abrasive media 530. In various embodiments, the rod 518 is positioned upstream of the mandrel 500 with respect to the direction of flow of the abrasive media 530. In various embodiments, the rod 518 may be replace with a cable, such as, for example, the cable 464 described above with reference to FIGS. 4A-4E, the cable being connected to the portion of the mandrel facing the direction of flow of the abrasive media 530.

In various embodiments, the mandrel 500 is sized with respect to the passageway 520 such that a gap 532 extends between an outer surface 534 of the mandrel 500 and an inner surface 538 of the passageway 520. In various embodiments, the gap 532 extends about the mandrel 500 and provides a narrow passage for the flow of abrasive media 530 to be forced along the inner surface 538 of the passageway 520, between the inner surface 538 and the outer surface 534 of the mandrel 500. Forcing the abrasive media 530 through the gap 532 results in the abrading effect of the abrasive media 530 to focus on the inner surface 538 of the passageway 520 rather than merely flowing through the interior or center of the passageway 520 where little to no abrasion occurs. In various embodiments, the gap 532 may have a non-dimensional dimension of one (1) to ten (10) one-hundredths the height or width of the mandrel 500. In various embodiments, the gap 532 may have a size equal from about five-hundred (500) microns (≈1.96 E-02 inches) to about five-thousand (5000) microns (≈1.96 E-01 inches).

In various embodiments, the passageway 520 is substantially straight along an axial direction—e.g., along the direction of flow of the abrasive media. In various embodiments, the passageway is curved, similar to the curved passageways described above. For curved passageways, a length 540 of the mandrel 500 is sized sufficiently to permit the mandrel 500 to traverse the curved passageway. While the mandrel 500 has been described having a specific geometry, the disclosure contemplates mandrel of other shapes and cross sections, with various numbers of protrusions or depressions extending from or within various surfaces of the mandrel, so the specific shape described above for the mandrel 500 should not be considered limiting.

Finally, it should be understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although various embodiments have been disclosed and described, one of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. Accordingly, the description is not intended to be exhaustive or to limit the principles described or illustrated herein to any precise form. Many modifications and variations are possible in light of the above teaching.

Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure. The scope of the disclosure is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. Different cross-hatching is used throughout the figures to denote different parts but not necessarily to denote the same or different materials.

Systems, methods and apparatus are provided herein. In the detailed description herein, references to “one embodiment”, “an embodiment”, “various embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments.

Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. 

What is claimed is:
 1. A method for smoothing surface roughness within a passageway, comprising: flowing an abrasive media through the passageway; and positioning a first mandrel within the passageway, the first mandrel being sized to create a gap between an outer surface of the first mandrel and an inner surface of the passageway, wherein the abrasive media is caused to flow through the gap, abrading the inner surface of the passageway.
 2. The method of claim 1, wherein the first mandrel is positioned at different locations within the passageway during a first smoothing operation.
 3. The method of claim 2, wherein positioning the first mandrel at different locations occurs through a passive process by action of friction between the outer surface of the first mandrel and the inner surface of the passageway.
 4. The method of claim 3, wherein the abrasive media is caused to flow in a forward direction followed by a reverse direction.
 5. The method of claim 4, wherein the first smoothing operation if followed by a second smoothing operation using a second mandrel, the second mandrel being sized larger than the first mandrel.
 6. The method of claim 2, wherein the first mandrel is connected to a cable configured to position the first mandrel at different locations.
 7. The method of claim 6, wherein the cable is connected to a cable reel configured to pay out the cable in a downstream direction.
 8. The method of claim 7, wherein the cable reel is configured to withdraw the cable in an upstream direction.
 9. The method of claim 8, wherein the passageway includes a circular cross section and the first mandrel is a first sphere.
 10. The method of claim 9, wherein a second sphere is connected to the cable adjacent the first sphere.
 11. The method of claim 1, wherein a first smoothing operation comprises traversing the first mandrel from an inlet of the passageway to an exit of the passageway followed by traversing the first mandrel from the exit of the passageway to the inlet of the passageway.
 12. The method of claim 11, wherein traversing the first mandrel from the exit of the passageway to the inlet of the passageway is caused to occur by withdrawing a cable connected to the first mandrel.
 13. The method of claim 11, wherein traversing the first mandrel from the exit of the passageway to the inlet of the passageway is caused to occur by reversing a flow direction of the abrasive media.
 14. The method of claim 11, wherein the first mandrel includes a non-spherical shape.
 15. An apparatus for smoothing surface roughness within a passageway, comprising: an abrasive flow machine configured to pump abrasive media through a component having the passageway; and a mandrel configured for variable positioning along a length within the passageway, the mandrel being sized to create a gap between an outer surface of the mandrel and an inner surface of the passageway.
 16. The apparatus of claim 15, wherein the mandrel is sized to enable friction between the outer surface of the mandrel and the inner surface of the passageway to control the variable positioning.
 17. The apparatus of claim 16, further comprising a cable reel and a cable connected to the mandrel and wherein the cable reel is configured to control the variable positioning.
 18. The apparatus of claim 17, wherein the passageway includes a circular cross section and the mandrel is a sphere.
 19. A method for smoothing surface roughness within a passageway, comprising: positioning a mandrel within the passageway, the mandrel being sized to create a gap between an outer surface of the mandrel and an inner surface of the passageway; flowing an abrasive media through the passageway in a first direction; and moving the mandrel in the first direction, wherein the abrasive media is caused to flow through the gap, abrading the inner surface of the passageway upstream of the mandrel.
 20. The method of claim 19, wherein the passageway and the mandrel have a non-circular cross section and wherein the positioning of the mandrel is controlled by a rod connected to a downstream portion of the mandrel. 